A conventional antenna array is a set of individual antennas used for transmitting and/or receiving radio waves, connected together in such a way that their individual currents are in a specified amplitude and phase relationship. The interactions of the different phases enhances the signal in one desired direction at the expense of other directions. This allows the array to act as a single antenna, generally with improved directional characteristics than would be obtained from the individual elements. A steerable array may be fixed physically but has electronic control over the relationship between those currents, allowing for adjustment of the antenna's directionality known as phased array antenna.
Hence, a phased array is an array of antennas in which the relative phases of the respective signals feeding the antennas are set in such a way that the effective radiation pattern if the array is reinforced in a desired direction and suppressed in undesired directions. In millimeter wave communications it is very important and necessary to compensate the high path loss by using a high gain antenna. A phase array antenna is expected to be a good candidate for 5G mmWave communications in order to achieve low cost and steerability.